This invention is directed to the field of high adhesion metal film pad stack compositions for microbridge air flow sensors.
The metal pad stacks are designed so that wire bond techniques or other connection can be made to the microbridge sensor at these pad stacks. High mechanical stresses can occur at these pad stacks so that a high adhesion of all layers of the stack is required. In the prior art the pad adhesion in microbridge air flow sensors is marginal due to the incorporation of platinum or nickel-iron (i.e., permalloy) sensor material as a part of the pad stack composite. In other words the pad areas in permalloy or platinum air flow sensors are potential sites for failure by reason of delamination. A typical prior art pad structure of a microbridge air flow sensor is shown in U.S. Pat. No. 4,683,159. U.S. Pat. No. 4,501,144 is another example. Both of these patents are also assigned to the assignee of the present invention. FIG. 1 of the U.S. Pat. No. 4,683,159 is reproduced herein as FIG. 1 and the teachings of the patent are incorporated by reference. Briefly in FIG. 1 there is shown an integrated semiconductor device comprising a semiconductor body 20, such as monocrystalline silicon, with a first surface 36 having a predetermined orientation with respect to a crystalline structure in the semiconductor body. The semiconductor body has a depression 30 formed into the first surface of the body. A layer(s) 28,29 of thin film dielectric material, such as silicon nitride (Si.sub.3 N.sub.4), covers at least a portion of the first surface. A thin film member 32,34 comprising the layer of dielectric material has a predetermined configuration bridging the depression. The member is connected to the first surface at substantially opposing ends of the predetermined configuration. The depression opens to the first surface along an edge 110,110a,110b,110c on each side of the member.
The thin film silicon nitride bridge members 32 and 34 include a pair of deposited thin film heat sensors 22 and 24, and a thin film heater 25. These deposited thin film resistive elements 22, 24, and 26 are preferably of platinum or Ni-Fe (permalloy) and the elements 22, 24, and 26 are generally encapsulated in the thin film of the silicon nitride comprising layers 28 and 29. Leads 92 connect the elements 22, 24, and 26 to pad areas 90 for electrically connecting the elements with other circuitry.
In the fabrication of the microbridge sensor devices, it was found necessary to design a new pad metal stack configuration to improve the pad adhesion.